The National Archives and Records Administration recently detected unauthorized activity on three desktops indicative of the same hack that extracted sensitive details on millions of current and former federal employees, government officials said Monday. The revelation suggests the breadth of one of the most damaging cyber assaults known is wider than officials have disclosed. The National Archives' own intrusion-prevention technology successfully spotted the so-called indicators of compromise during a scan this spring, said a source involved in the investigation, who was not authorized to speak publicly about the incident. The discovery was made soon after the Department of Homeland Security's...